Sewing machine for sewing a rubber strip

ABSTRACT

Sewing machine for sewing a rubber strip to a tubular end piece of a garment made from an elastic textile material in order to produce an endless elastic band. The sewing machine comprises a presser foot (18) with an insertion opening (22) for the rubber strip (24), a braking device (48) to resist the insertion movement of the rubber strip and provided with two clamping elements (50, 52) which grip the strip, and a cutting system (26) which can be motor driven in order to cut the rubber strip. To eliminate the reintroduction process of the strip (24) into the insertion opening (22) of the presser foot (18) after said cutting, the cutting system (26) is arranged rear from the insertion opening (22) of and in the presser foot (18), and a drive (56) is associated with the braking device (48) to increase the gap between the two clamping element (50, 52) just before actuation of the cutting system (26).

The present invention relates to a sewing machine for sewing a rubberstrip to a garment.

German DE-OS No. 34 10 181 discloses a sewing machine in which a cuttingsystem is used to cut a rubber strip arranged between a braking deviceand an insertion opening of the presser foot. This known sewing machinealso has an additional braking device between the cutting system and thepresser foot, and has a drive system thereof. The additional brakingdevice is not actuated during insertion of the rubber strip, and isactuated immediately before actuation of the cutting system to hold thecut rear end of the rubber band under tension. After sewing the cut rearend of the rubber strip to the garment, it is necessary to insert theforward end of the rubber strip in the insertion opening of the presserfoot. The forward end of the rubber strip is moved with the garment tothe transporter. The condition that after forming each endless elasticband of the rubber strip, inserting the forward end into the insertionopening of the presser foot must be renewed, presents a very high workdelay.

The object of the present invention is to improve the above-mentionedsewing machine, such that after cutting the rear end of each sewn rubberstrip, the renewed insertion of the rubber band into the insertionopening of the presser foot is eliminated.

By the present invention, it is attained that after cutting the rear endof each sewn rubber strip, the forward end portion of the rubber stripcoming from stock remains in the presser foot and therefore it isunnecessary to renew the insertion thereof.

One embodiment of the present invention is shown in the drawings andwill be described later. In the drawings:

FIG. 1 is a schematic illustration of essential parts of a sewingmachine, according to the present invention; and

FIGS. 2a and 2b are schematic illustrations of a cutting device to cut arubber strip.

FIG. 1 shows a schematically shown side view of a sewing machine whichis especially suited to sew a rubber strip to a tubular end piece of agarment made from an elastic textile material to produce an endlesselastic band. As an under-support for sewing material, a base plate 10is rigidly secured with the frame of the sewing machine. In an openingof the base plate 10, a transporter 12 to feed the sewing material ismovably supported as known. The base plate 10 has also an opening 14 toreceive a sewing needle 16. The electric drive for the transporter 12and the sewing needle is known, and is not shown in the drawing for sakeof clarity. A presser foot 18 is in the frame of the sewing machineupward and downward movably supported perpendicular to the base plate10. A pneumatic cylinder 20 drives the presser foot 18, and is securedwith the frame of the sewing machine and the piston rod thereof isconnected with the presser foot 18. A forward portion of the pressurefoot 18 has an insertion opening 22 for an elastic strip, that is, arubber strip, 24 for an elastic strip which is supplied from a stock(not shown). In the presser foot 18, a cutting system 26 to cut therubber strip is mounted, and the construction thereof will be describedlater.

As shown especially in FIGS. 2a and 2b, the cutting system 26 comprisesa cylinder 30 which is rotatably supported in a case 32. The case 32 isnon-rotatably secured in the presser foot 18, and has diametricallyopposed slits 34 and 36 which align with an inlet opening 22 and with anoutlet opening of the presser foot 18 respectively. When the presserfoot 18 has no outlet opening, the slit 36 of the case 32 acts as theoutlet opening. The cylinder 30 has a through passage 38, and the wallof inlet side is funnellike tapered. Clearly, the outlet side of thepassage 38 aligns only at a predetermined angle position of the cylinderwith the outlet slit 36 of the case 32, whereas the inlet side of thepassage aligns with the inlet slit 34 of the case 32 over a large anglerange of the cylinder 30 by the conical widening. In the presser foot18, a cutting knife 40 is mounted, and the cutting edge thereof is nearthe outlet slit 36 of the case 32. To rotate the cylinder 30 relative tothe case 32, a pneumatic cylinder 42 is supported to the frame of themachine, and a piston rod 44 thereof is pivotably connected with thecylinder 30 by radially extending arm. The length of the piston rod 44is determined that the up and down movement of the presser foot 18results in no remarkable rotation of the cylinder 30.

Thus, the rubber strip 24 supplied from a stock, not shown, is sewn bythe sewing needle 16 between the presser foot 18 and the transporter 12with supplied garment textile material 46, and it is necessary that therubber strip 24 must be supplied in stretched state. To the purpose, atsuitable distance over the presser foot 18, a brake 48 is mounted. Thebraking device 48 has two clamping elements 50 and 52 between which therubber strip 24 is clamped. The clamping element 52 which has an openingto receive the rubber strip 24 is formed as double arms link and ispivotably connected with the clamping element 50. The clamping element52 is urged to the clamping element 50 by a compression spring 54. Thepreload force of the compression spring 54 is regulated to adaptrequirement to applied brake force by both clamping elements 50 and 52to the rubber strip 24 and also the tension of the rubber strip 24. Thefree end of the clamping element 52 spaced from the presser foot 18 ispivotably connected to a piston rod of a pneumatic cylinder 56 which inturn is connected to the clamping element 50. By retracting the pistonrod into the pneumatic cylinder 56, the movable clamping element 52rotates against the force of the compression spring 54 so that the forceis relieved.

As shown in FIG. 1, the clamping element 50 is rotatably connected tothe frame of the machine in the direction of feeding the textilematerial 46, rearward from the presser foot 18 and approximately to theheight. By the connection of the clamping element 50, the free end ofthe clamping element 50 moves substantially to the direction of theinlet opening 22 of the presser foot 18 when the element rotates. Torotate the clamping element 50, a pneumatic cylinder 58 mounted to theframe of the machine and the piston rod thereof is pivotably connectedwith the clamping element 50 spaced from the rotating point.

A compressed air nozzle 60 is arranged in the base plate 10 to directair toward the forward end of the presser foot 18, and is suitablyarranged adjacent to the lower side of the presser foot. The compressedair discharged from the nozzle 60 ends at the forward end of the rubberstrip 24 projected from the lifted presser foot 18 rearward to thetransporter 12. In piping connecting the compressed air nozzle 60 with acompressed air source, a magnetic valve, not shown, is inserted, suchthat the air path is opened only when the presser foot is in liftedposition. Of course, it is not necessary to arrange the compressed airnozzle 60 as shown, it may be arranged otherwise to bend the free end ofthe rubber strip by the compressed air stream rearward along the underside of the presser foot.

The pneumatic cylinders 20, 42, 56 and 58 are connected through piping,not shown, with a compressed air source. In each piping, a magneticvalve is inserted to control by foot switch operated by an operator. Bycorresponding operation of the foot switches, magnetic valves for thepneumatic cylinders 20 and 58 are simultaneously opened and closed. Thearrangement is provided thereby such that the pressure variation in thepneumatic cylinders 42 and 58 relative to the pneumatic cylinders 56 and20 have predetermined delay. This can be done simply that the piping tothe pneumatic cylinders 42 and 58 insert throttle.

The operation of the above-described sewing machine will be described.

At first, it is assumed that the presser foot 18 is in lift position,the engaged braking device 48 is in lower position, and the cuttingsystem 26 is in non-operating position, and that a free end of therubber strip 24 is projected from the lower side of the presser foot 18.As the presser foot 18 is in lift position, the compressed air nozzle 60is connected with compressed air source, so that the free end of therubber strip 24 projected from the presser foot 18 turns rearward alongthe underside of the presser foot 18. By corresponding operation of thefoot switch, the pneumatic cylinder 20 is supplied with compressed airto lower the presser foot 18, so that the presser foot presses and holdsthe rubber strip 24 on the textile 46 which is on the base plate 10. Theoperation of the foot pedal results that the pneumatic cylinder 58 issupplied by compressed air at the same time, with a predetermined delay,so that the braking device 48 pivots upwards as a whole from the presserfoot 18, and the end portion of the rubber strip 24 is tensioned. Whilethe position of the presser foot 18 and the braking device 48 ismaintained, suitable operation of foot switch actuates the drive for thetransporter 12 and the sewing needle 16, so that the stretched staterubber strip 24 is sewn with the textile 46 successively. Meanwhile thebraking device 48 presses, i.e. the movable clamping element 52 is urgedto the clamping element 50 by the force of the compression spring 54 sosupply braking force to the rubber strip 24 which is fed in stretchedstate. Then, from the textile material 46, tubular end portion of agarment, e.g. leg portion of a bath suit, having elastic band can beformed by the above-mentioned way. Shortly before the sewing rubberstrip to the textile material overlap the forward end thereof, whichoccurs at the forward end of the presser foot 18, by suitable operationof foot switch, the pneumatic cylinder 56 actuates by compressed air torelease the braking device 48, so that the forward end portion of thesupplied rubber strip 24 is tensionless. The operation of the footswitch results that the pneumatic cylinder 42 is supplied by compressedair at the same time, with certain delay, so that the cylinder 30rotates relative to the case 32 of the cutting system 26 from theposition shown in FIG. 2a to FIG. 2b. Then, the rubber strip in thepassage 38 of the cylinder 30 is pressed to the edge of the cuttingknife 40 and is separated. The tensionless rear end portion of therubber strip 24 will be sewn with the garment 46, so that it will sewnoverlapping the forward end portion which had sewn in stretched state.As the distance between the cutting knife 40 and the sewing needle 16,in practice under 20 mm, the overlapping is very short and materialsaving can be attained. The sewing process is end, and an endlesselastic band is formed in the garment. By suitable operation of footswitch, drive of the transporter 12 and the sewing needle 16 is stopped,and the cutting system 26 inoperative, and the braking system 48 returnsto operative position. Then, by suitable operation of foot switch, thepneumatic cylinders 20 and 58 is supplied with compressed air, so thatthe presser foot 18 raises, and the whole braking system 48 pivotsdownward with predetermined delay. The result is such that the forwardend portion of the rubber strip 24 which was in the presser foot 18projects from the presser foot and by influence of now injectedcompressed air from the nozzle 60, moves rearward along the lower sideof the presser foot. Now the sewing machine is ready to start new sewingprocess to form an endless elastic band.

Apart from the shown embodiment, the pneumatic cylinder which serves tooperate the cutting system may be secured with a presser foot supportingpivot arm. The pneumatic cylinder in this case has no effect to thecutting system by operation of the pivot arm and the presser foot.

Such embodiment has constructional advantage compared with the shownembodiment, such that forward and both sides of the presser foot arekept free. Then, the operator can perform sewing process opticallywithout disturbance, and the material can be introduced by fingersdirectly. Thus, very precise sewing of the rubber strip along thematerial edge can be performed.

I claim:
 1. Sewing machine for sewing an elastic strip to a garment madefroma sewing material, said sewing machine comprising a sewing needle, apresser foot for pressing the sewing material to a base plate and havingan insertion opening for the elastic strip and movable up and down bymotor drive relative to the base plate, a transporter mounted in thebase plate to transport the sewing material, a guide device to guide theelastic strip to the presser foot, a braking device to resist guidemovement of the elastic strip and provided with two clamping elementswhich grip the elastic strip, and a motor driven cutting system to cutthe elastic strip and mounted between the braking device and the sewingneedle, characterized in that the cutting system (26) is arrangedbetween the insertion opening (22) in the presser foot (18) and thesewing needle, and that the braking device (48) has a drive (56) inorder to increase the gap between the two clamping elements (50, 52)immediately before actuation of the cutting system (26).
 2. Sewingmachine according to claim 1, in which the cutting system (26) consistsof a cylinder (30) rotatably journalled in the presser foot (18) andhaving a diagonal guide slit (38), a cutting knife (40) fixed to thepresser foot (18), and a drive (42) for rotation of the cylinder (30).3. Sewing machine according to claim 1 or 2, in which a compressed airnozzle (60) is mounted to direct air in the feeding direction of theelastic strip (24) along the under side of the presser foot (18).
 4. Asewing machine for sewing an elastic strip to a piece of material, saidsewing machine comprising presser foot means for pressing a portion ofthe elastic strip against the piece of material, said presser foot meansincluding means for defining an insertion opening through which theelastic strip extends, gripper means for gripping a portion of theelastic strip before the gripped portion of the elastic strip enters theinsertion opening to enable the elastic strip to be tensioned andstretched, needle means for sewing the stretched elastic strip to thepiece of material while said presser foot presses the stretched elasticstrip against the piece of material and while said gripper means gripsthe elastic strip, said gripper means being operable to release theelastic strip to eliminate tension in the elastic strip after a portionof the elastic strip has been sewn to the piece of material, cuttermeans for cutting the tensionless elastic strip after the elastic striphas been sewn to the piece of material, said cutter means being operableto cut the tensionless elastic strip at a location between the insertionopening in said presser foot and said needle means so that a portion ofthe elastic strip extends through the insertion opening in said presserfoot after the elastic strip has been cut by said cutter means.
 5. Asewing machine as set forth in claim 4 further including means formoving said gripper means away from said presser foot to stretch theelastic strip.